The present invention relates to a method of operating a long-term blood pressure measurement device having a measurement sensor for detecting a pulse wave signal, having a measurement sensor for body current signals, having a pressure cuff for a non-invasive determination of the blood pressure, having a control and evaluation unit for determining blood pressure values, on the one hand from signals acquired by means of the pressure cuff (pressure cuff signals), and, on the other hand from a pulse wave transit time that is derived from body current signals and pulse wave signals, and having a memory for storing blood pressure values.
Such devices have been known for some time and are used e.g. in mobile form to be worn on the body of persons over comparatively long time periods of several hours or several days. In known devices, blood pressure measurements as a rule take place periodically at fixedly predefined time intervals, e.g. every 15 or 30 minutes. This has the result in a disadvantageous manner that significant blood pressure changes remain unrecognized when they occur in the time intervals between two measurements. Furthermore, with regularly occurring measurements, unnecessary measurements are also carried out with unchanged blood pressure values, with these measurements then putting unnecessary stress on or unnecessarily irritating the persons wearing the device.
With known devices of the named kind that are equipped with a measurement sensor for detecting a pulse wave signal, a blood pressure measurement can advantageously be triggered via the pressure cuff not only at regular time intervals, but also in dependence on the progression of the pulse wave signal. A blood pressure measurement can therefore always be triggered via the pressure cuff, for example, when there is an indication of a noticeable blood pressure value due to the progression of the pulse wave signal. Such a long-term blood pressure measurement device is described, for example, in the German patent application DE 10 2007 050 598.3. For example, the fact that the pulse wave signal is detected via a measurement sensor that has to be fixed to the finger or to the earlobe of a person, which is often irritating for the person, in particular in daily life, and which also frequently results in artifacts in the pulse wave signal due to movements of the person, is a disadvantage of this long-term blood pressure measurement device.
It is furthermore a disadvantage in the mentioned long-term blood pressure measurement device that the actual measurement of the blood pressure takes place via the pressure cuff, which for persons is associated with a high pressure on the upper arm, on the one hand, and with a comparatively loud noise of the compressed air source acting on the pressure cuff, on the other hand. This has an irritating effect in everyday life and can also have the result that blood pressure values are falsified since some people are agitated by the blood pressure measurement they can clearly perceive, which then results in increased values and ultimately in values unrealistic for a normal everyday situation.
It is furthermore known to use devices of the initially named kind such that blood pressure values are determined in long-term operation only from the pulse wave transit time by means of different calculation methods, with a blood pressure measurement by means of the pressure cuff only being used for an initial calibration or for a later recalibration. The calculation and calibration methods used here, however, disadvantageously frequently result in falsified blood pressure values.